The field of orthodontics is concerned with repositioning and aligning a patient's teeth for improved occlusion and aesthetic appearance. For example, orthodontic treatment often involves the use of tiny slotted appliances, known as brackets, which are fixed to the patient's anterior, cuspid, and bicuspid teeth. An archwire is received in the slot of each bracket and serves as a track to guide movement of the teeth to desired orientations. The ends of the archwire are usually received in appliances known as buccal tubes that are secured to the patient's molar teeth.
A number of orthodontic appliances in commercial use today are constructed on the principle of the “straight wire concept” developed by Dr. Lawrence F. Andrews, D.D.S. In accordance with this concept, the shape of the appliances, including the orientation of the slots of the appliances, is selected so that the slots are aligned in a flat reference plane at the conclusion of treatment. Additionally, a resilient archwire is selected with an overall curved shape that normally lies in a flat reference plane.
When the archwire is placed in the slots of the straight wire appliances at the beginning of orthodontic treatment, the archwire is often deflected upwardly or downwardly from one appliance to the next in accordance with the patient's malocclusions. However, the resiliency of the archwire tends to return the archwire to its normally curved shape that lies in a flat reference plane. As the archwire shifts toward the flat reference plane, the attached teeth are moved in a corresponding fashion toward an aligned, aesthetically pleasing array.
A position of the bracket on a tooth as well as the interaction between the bracket and an archwire affects a resulting position of the tooth. As can be appreciated, it is important for the practitioner using straight wire appliances to precisely fix each bracket in the proper position on the corresponding tooth in order to achieve the desired tooth movement. If, for example, a bracket is placed too far in an occlusal direction on the tooth surface, the archwire will tend to position the crown of the tooth too close to the gingiva (gums) at the end of the treatment. As another example, if the bracket is placed to one side of the center of the tooth in either the mesial or distal directions, the resultant tooth orientation will likely be an orientation that is excessively rotated about its long axis.
The process of positioning and bonding the brackets to the patient's teeth often requires a practitioner to visually determine the proper location of the brackets on the respective teeth based on an estimate of how the brackets will affect the movement of the teeth. There is typically no way to confirm whether the selected bracket placement will result in the desired tooth movement. Similarly, there is typically no way to select a desired position for a tooth and subsequently select the location of a bracket on the tooth based on the desired position of the tooth.
The state of the art in orthodontics is rapidly moving toward digital and computer-aided techniques. These techniques include the use of intra and extra-oral scanners, three-dimensional (3D) modeling of a tooth structure, and fabrication of orthodontic appliances from digital data.